Signal Transducer and Activator of Transcription (STAT) proteins are a family of transcription factors essential for the function of growth factor and cytokine signaling pathways. Stat4, which is activated by IL-12 and IL-23, is critical in the generation of inflammatory responses in vivo. However, the specific functions of Stat4 during inflammatory responses are still unclear. In the previous grant periods, we established roles for Stat4 isoforms in IL-12 responses and inflammatory disease, defined Stat4-dependent chromatin alteration during programming of Th1-specific expression, and defined new roles for Stat4 in the development of inflammatory and regulatory T cell subsets. We have further demonstrated that the function of T-bet, the master regulator of the Th1 phenotype largely relies on Stat4 for its' ability to activate gene expression. In the next proposed period of funding, we will continue our focus on defining the role of Stat4 in cytokine responses and transcriptional control during inflammatory cell differentiation. We will test the hypothesis that Stat4 functions as a central component in the development of inflammatory immunity by coordinating signals from multiple cytokines to confer long lasting changes in gene expression. This will first be explored by defining the sequence of epigenetic modifications, and the requirement for specific enzymes mediating epigenetic modifications, in the Stat4-dependent programming of genes for expression in Th1 cells. We will examine the role of Stat4 in maintaining Th17 responses and the development of allergic inflammation using novel reagents to isolate and track Th17 cell fate. Finally, in a translational Aim, we will define the association of Stat4 isoforms with inflammatory disease in patients with inflammatory bowel disease. Together, these studies will elaborate new information, at the level of genetic regulation, cellular differentiation in mouse models of allergic inflammation, and in patient samples, regarding the regulation of inflammatory immunity and the ability to manipulate immunity in patients with inflammatory disease. PUBLIC HEALTH RELEVANCE: T cell mediated inflammation is required for immunity to many pathogens but also is a critical component of autoimmune disease. These studies focus on a transcription factor, Stat4, which controls T cell function. The experiments described in this proposal will examine the function of Stat4 in controlling gene expression, in T cell differentiation in vivo using mouse models, and in patient samples towards the goal of understanding how this factor regulates inflammation and identify pathways that may be targeted for pharmaceutical intervention.